Docassemble

Fixed
- `get_question_data()` and related functions raised exception.
- Let's Encrypt renewal error.

Added
- The `advance_progress_meter` option for the `/api/session` POST API
endpoint.
- The `DAWEBSERVER` Docker environment variable and the `web server`
Configuration directive.
- The `S3ENDPOINTURL` Docker environment variable and the `endpoint
url` Configuration directive under `s3`.
Changed
- Upgrade Docker OS to Debian buster.
- Upgrade Python from 3.5 to 3.6.
- The default web browser under Docker is now NGINX.
- The Docker image now builds in two parts. The jhpyle/docassemble-os
image is the base image for jhpyle/docassemble.
- The `get_session_variables()` and `set_session_variables()`
functions use the current user's decryption key by default.

Fixed
- Setting of `__version__` in Python 2.7 raised Unicode error.
- Back button after action in URL repeated the action.
- The `progress` value was missing from the JSON representation of the
question.

Added
- The `SQLObject` class.
- The `input type` called `ajax`.
- The `paragraphs` Jinja2 filter.
Changed
- The `__version__` variable is now defined in packages generated from
the Playground packages folder.
- UTM parameters are retained if an `analytics id` is defined under
`google` in the Configuration, or a `segment id` directive is
defined in the Configuration.
- The Playground packages folder GitHub commit process now uses `git
merge` to merge changes, which means it might fail if a commit would
overwrite changes.
- The Playground packages folder now allows for committing to a new
remote branch.
Fixed
- Incorrect behavior during initial visit to `/interview` when
interview uses unique sessions.
- Interview advanced a step despite `validation code` raising an
exception.

Added
- The `features` option `labels above fields`.
Fixed
- Errors with `sessions are unique` and `required privileges`.

Added
- The `enable playground` Configuration directive.
Changed
- The behavior of the `label` option of `list collect` no longer
prints text before `1.`, `2.`, etc. Now the `label` supplies the
whole label for the item, and it can include the number by way of
the index variable.
Fixed
- The `list collect` feature raised an exception when the field
definition included Mako substitution.
- Non-required upload fields were creating zero-byte files on some
servers.